Plastic double nut mechanism enabling rigid orthopedic distraction

ABSTRACT

A distraction apparatus for an external fixation device used to rigidly immobilize bone fragments during bone lengthening and angular deformity correction includes distractor mechanisms and pivotable spacers for connecting frame members of an external fixator, and wire and half pin fasteners. The interconnected distractor mechanisms, pivotable spacers and frame members form a rigid structure with rigidity which is maintained during adjustment of the distraction. For linear distraction, the distraction mechanism is a single screw assembly with a single-threaded rod and dual plastic nuts disposed either side of a metallic adjustment surface. After tightening down, the nuts may be synchronously co-rotated, advantageously using a tool such as a double wrench engaging on aligned faces of the nuts. This synchronous co-rotation causes linear displacement along the threaded rod, thereby enabling distraction. Further, the metal-to-plastic inter-face between the nuts and the adjustment surface facilitates this synchronous co-rotating without causing loosening of the nuts, thereby minimizing the introduction of play in the mechanism during distraction.

RELATED APPLICATIONS

The application is a continuation of U.S. application Ser. No.08/448,922, filed May 25, 1995, which is a divisional of abandoned U.S.application Ser. No. 08/075,179 filed Jun. 10, 1993.

BACKGROUND OF THE INVENTION

The present invention relates to external fixation devices, and inparticular, to distractor mechanisms and hinges for external fixationdevices.

External fixation of bone fractures is well known in the art. Manydifferent external fixation devices have been developed, virtually allof which in one form or another use multiple transverse fixation wiresor half-pins which extend through, or are embedded in, respectively, thebone and soft tissue surrounding the bone, and connect to various typesof supporting elements, such as rings, half-rings, arches or bars.

Aside from providing stable fixation of bone fragments to promote properfracture healing, external fixation devices also provide means fortransporting the bone fragments in order to correct length discrepanciesor angular deformities of the bone. One of the more common externalfixation devices used for such purposes, often referred to as theIlizarov External Fixator, includes three basic elements: multiple rings(or arches) disposed coaxially about the bone segments to be fixated;transverse wires or half-pins for fixating the bone segments to therings (or arches); and distractor mechanisms. For angular distraction,the external fixator further includes pivots, or hinges, to define anaxis of rotation perpendicular to the plane of the bone deformity toallow rotation of the bone segment.

Hence, for linear distraction, a typical basic assembly includesproximal and distal rings, or ring sets, connected by three or fourdistractor mechanisms; and for angular distraction, a typical basicassembly includes proximal and distal rings, or ring sets, connected bytwo hinges and one distractor mechanism.

A conventional distractor mechanism for linear distraction consists of athreaded rod which is fastened to each of the rings by the use of doublenut assemblies, i.e. nuts which are threaded onto the rod and tightenedagainst either side of each ring. A conventional distractor mechanismfor angular distraction consists of two hinge segments which arefastened to the proximal and distal rings, and are coupled to each othervia a threaded distraction rod. A conventional basic hinge assembly usedfor angular distraction consists of two hinge segments which arefastened directly to the rings and connected to each other with a nutand bolt.

The current conventional external fixator elements (distractors andhinges) present a number of problems. First, because the connectionpoints for the distractor mechanisms and hinge assemblies, i.e. theholes in the rings and hinge members, must be slightly larger than thediameter of the threaded component (rods and bolts), the resultingassembly is always unstable. In other words, during installation,adjustment or distraction, a certain amount of mechanical "free play"will be present. During the treatment period of the patient, this canand often does cause pain.

Currently, there are two methods used in seeking to compensate for thisproblem. One method is to loosen and retighten all hinge and distractornuts before and after each angular correction or linear distractionmaneuver. This can be effective, but is time consuming and frustratingfor the patient. Plus, the torque which must be applied to loosen andretighten the hardware can adversely affect the healing process andcause pain for the patient. The second method involves the use of nylocknuts in the hinges and distractor mechanisms to achieve some degree ofradial stability by imposing an axial preload on the rotating elements.The mechanical "free play" is still there, but is damped by frictionalforces from the fasteners. However, even when the hinge is preciselyadjusted, the potential for an unstable frame is still present due tothe over-sized hole diameters.

A second problem arises during each distraction maneuver, particularlyduring an angular distraction. Each incremental distraction takes agreat deal of time, and the procedure is generally too complex for youngpatients to perform reliably. With so many components, i.e. plates,hinge segments, rods, bolts and nuts, to loosen, turn and retighten, itis difficult for the patient to remember the adjustment sequence andmaintain a consistent distraction rate. Moreover, if any of the nuts areaccidentally left untightened, instability, and therefore, pain anddelayed healing, can result.

Accordingly, it would be desirable to have an external fixation devicewith a distraction mechanism which allows adjustable distraction whilesimultaneously providing a rigid structure, i.e. both radial and axialstability of the overall assembly.

SUMMARY OF THE INVENTION

A linear distractor mechanism in accordance with a preferred embodimentof the present invention includes a single-threaded screw distractor anda rotatable connector. The single-threaded screw distractor connects tothe proximal and distal external fixator frame members, and rigidly andadjustably disposes the external fixator frame members at a separationdistance which is linearly adjustable. The rotatable connectorrotatively connects the single-threaded screw distractor to one of theexternal fixator frame members. The interconnected single-threaded screwdistractor, rotatable connector and external fixator frame members forma rigid structure with a rigidity which is maintained during theadjusting of the separation distance between the frame members.

A preferred embodiment of the single-threaded screw distractor is atelescoping assembly with a single-threaded rod and a like-threaded,rotatable, coaxial sleeve. A preferred embodiment of the rotatableconnector is a fastener assembly with a bolt and a pair of plasticwashers, wherein the plastic washers are disposed on opposing sides ofone of the external fixator frame members and the bolt extendstherethrough and threads into the single-threaded screw distractor. Analternative preferred embodiment of the rotatable connector is afastener assembly with a pair of threaded, plastic nuts, wherein thethreaded, plastic nuts are disposed on opposing sides of one of theexternal fixator frame members and the single-threaded screw distractorextends and threads therethrough.

A linear distractor mechanism in accordance with an alternativepreferred embodiment of the present invention includes a rod, base andadjustable connector. The rod connects to one and the base connects tothe other of the external fixator frame members. The adjustableconnector adjustably connects the rod to the base to rigidly andadjustably dispose the external fixator frame members at a separationdistance which is linearly adjustable. The interconnected rod, base,adjustable connector and external fixator frame members form a rigidstructure with a rigidity which is maintained during the adjusting ofthe separation distance between the frame members.

A preferred embodiment of the rod is a threaded rod. A preferredembodiment of the base is a hollow sleeve for coaxially receiving therod. A preferred embodiment of the adjustable connector is a plasticfastener assembly with a pair of threaded plastic nuts for dispositionon opposing sides of an extended portion of the base with the rodextending and threading therethrough. An alternative preferredembodiment of the adjustable connector is a fastener assembly with abracket coupled to the base and a pair of threaded plastic nuts fordisposition on opposing sides of a portion of the bracket with the rodextending and threading therethrough. Another alternative preferredembodiment of the adjustable connector is a plastic fastener assemblywith a threaded plastic member rotatably captured within the base forthreaded engagement with one end of the rod.

An angular distractor assembly in accordance with the present inventionincludes a distractor, a pair of pivotable connectors, and a pair ofpivotable spacers. The distractor, via the pivotable connectors,connects the proximal and distal external fixator frame members, andrigidly and adjustably disposes the frame members at an angularorientation with respect to one another. One pivotable connectorpivotally connects a portion of the distractor to one of the externalfixator frame members, and another pivotable connector pivotallyconnects another portion of the distractor to the other frame member.The pivotable spacers pivotally connect and separate the externalfixator frame members. The interconnected distractor, pivotableconnectors, pivotable spacers and external fixator frame members form arigid structure with a rigidity which is maintained during adjustment ofthe angular orientation between the frame members.

A preferred embodiment of the distractor is a single-threaded, rotatablerod which is rotatively engaged with one of the pivotable connectors andthreadedly engaged with the other pivotable connector. A preferredembodiment of the pivotable connector is a metal and plastic pivotassembly including a metal bracket with a pivotable, plastic insert. Apreferred embodiment of the pivotable spacer is a metal spacer and ametal and plastic pivot assembly. The metal spacer includes a rod with aportion for engaging the metal and plastic pivot assembly and anotherportion for connecting to one of the external fixator frame members. Themetal and plastic pivot assembly includes a metal bracket for connectingto the other external fixator frame member and a pivotable, plasticinsert for engaging the rod.

These and other features and advantages of the present invention will beunderstood upon consideration of the following detailed description ofthe invention and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an external fixator with a preferred embodiment of alinear distractor assembly in accordance with the present invention.

FIG. 2 illustrates a cross-section (along line 2--2) of one of thelinear distractor mechanisms of FIG. 1.

FIGS. 3A and 3B illustrate a ratchet assembly which can be used on thelinear distractor mechanisms of FIG. 1.

FIG. 4 illustrates an external fixator with an alternative preferredembodiment of a linear distractor assembly in accordance with thepresent invention.

FIG. 5 illustrates a further alternative preferred embodiment of alinear distractor assembly in accordance with the present invention.

FIG. 6 illustrates a cross-section (along line 6--6) of the lineardistractor mechanism of FIG. 5.

FIG. 7 illustrates a still further alternative preferred embodiment of alinear distractor assembly in accordance with the present invention.

FIG. 8 illustrates a cross-section (along line 8--8) of the lineardistractor mechanism of FIG. 7.

FIG. 9 illustrates an external fixator with an angular distractorassembly in accordance with an alternative preferred embodiment of thepresent invention.

FIG. 10 illustrates a cross-section (along line 10--10) of the angulardistractor mechanism of FIG. 9.

FIG. 11 illustrates a cross-section (along line 11--11) of the adjustormechanism on the angular distractor mechanism of FIG. 10.

FIG. 12 illustrates a cross-section (along line 12--12) of the adjustormechanism of FIG. 11.

FIG. 13 illustrates an external fixator with an angular distractorassembly in accordance with an alternative preferred embodiment of thepresent invention.

FIG. 14 illustrates a cross-section (along line 14--14) of one of thepivotable spacer mechanisms of FIG. 13.

FIG. 15 illustrates a top view perpendicular to the plane of the upperframe member of the external fixator of FIG. 13.

FIG. 16 illustrates the wire and pin fastener assembly used on the framemembers of the external fixators of FIGS. 1, 4, 5, 7, 9 and 13.

FIG. 17 illustrates a side view of the fastener assembly of FIG. 16while fastening a wire to one of the external fixator frame members.

FIG. 18 illustrates a side view of the fastener assembly of FIG. 16while fastening a pin to one of the external fixator frame members.

DETAILED DESCRIPTION OF THE INVENTION

Referring to FIG. 1, an external fixator assembly 100a for performinglinear distraction with a preferred embodiment of a linear distractorassembly in accordance with the present invention includes lineardistractor mechanisms 102a, and upper 106 and lower 108 external fixatorframe members, or rings. Each ring 106, 108 includes multiple, spacedholes 110, a number of which are used for mounting fastener assemblies112 (discussed further below) for fastening transverse wires 114 and/orhalf-pins 116. These wires 114 and/or half-pins 116 pass through or areanchored into, respectively, the bone segments 118a, 118b which are tobe externally fixated with the fixator assembly 100a.

Each distractor mechanism 102a includes a single-threaded rod 120 whichis coaxially mated with an internally like-threaded, plastic insert 128mounted within a rotatable sleeve 122. The rod 120 is fastened to theupper ring 106 by extending it through one of the holes 110 and havingtwo nuts 126a, 126b tightened against opposing sides of the ring 106.The sleeve 122 is rotatively connected to the lower ring 108 by way of arotatable connector 124 (discussed further below). At approximately themidway point of the sleeve 122, is a recessed, square portion 130 whichcan be used as a tool interface for mating with a tool (e.g. a wrench134) for rotating the sleeve 122.

The distractor mechanisms 102a can also include a ratchet assembly 132(as shown in FIGS. 3A and 3B, and discussed further below). This ratchetassembly 132 prevents rotation of the sleeve 122 in a selecteddirection.

Referring to FIG. 2, the construction of a linear distractor mechanism102a in accordance with the present invention can be understood. Themetal-to-plastic interface of the threaded rod 120 and like-threadedplastic insert 128 can be seen in cross-section. The plastic insert 128is pressed into the end 122a of the rotatable sleeve 122 which iscounterbored, and is prevented from rotating within or being pulled outfrom the sleeve 122 by crimping the tip 122b of the sleeve 122 (e.g. ina pyramidal shape) after the insert 122 has been pressed therein.

Referring still to FIG. 2, the rotatable connector 124 can be betterunderstood. The rotatable sleeve 122 is connected to the bottom ring 108by placing plastic washers 124a and 124b on opposite sides of the ring108, and passing a bolt 124c through the ring hole 110 and plasticwashers 124a, 124b to be mated with internal locking threads 122c (e.g.screw thread inserts produced under the trademark HELI-COIL®) of thesleeve 122. The bolt 124c is then tightened down within the sleeve 122and against the plastic washers 124a, 124b to eliminate any axial freeplay between the ring 108 and sleeve 122. These internal locking threads122c prevent the bolt 124c from turning independently from the sleeve122. This prevents the union of the bolt 124c and sleeve 122 frombecoming overly tight (which would inhibit rotation of the sleeve 122)or loose (which would introduce undesirable axial free play between thering 108 and sleeve 122). The plastic washers 124a, 124b are compressedby the tightened bolt 124c and significantly reduce friction, therebyassisting in setting and maintaining an appropriate preload between themetal bolt 124c, rotatable sleeve 122 and ring 108.

Due to the metal-to-plastic interfaces of the sleeve 122, plastic washer124a and ring 108, and of the bolt 124c, plastic washer 124b and ring108, the sleeve 122 can be selectively rotated while simultaneouslyforming and maintaining a rigid structure with respect to the lower ring108. This rigidity is further maintained by the metal-to-plasticinterface of the threaded rod 120 and plastic insert 128, as the metalrod 120 remains fixed, and therefore rigid, with respect to the upperring 106.

The threaded rod 120 has a hexagonal socket 120a in the end tofacilitate rotation of the rod 120 into or out of the sleeve 122 by useof a conventional hexagonal key wrench (not shown). Such adjustments areoften necessary when initially adjusting or attaching a lineardistractor mechanism 102a to the rings 106, 108, since the interfacebetween the plastic insert 128 and the threaded rod 120 is sufficientlytight as to require more than finger pressure on the rod 120 to rotateit into and out of the sleeve 122. However, the larger diameter of therotatable sleeve 122 provides sufficiently greater leverage thatordinary finger pressure is sufficient to rotate the sleeve 122 on therod 120 once the rod 120 is secured to the ring 106 with the nuts 126a,126b.

Referring to FIGS. 3A and 3B, the ratchet assembly 132 can be betterunderstood. The ratchet assembly 132 includes a circular collar 132a,which is fixed about the rotatable sleeve 122 via compression with ahexagonal socket set screw 132b. This circular collar 132a sits atop anarcuate collar 132c which is also coaxial with the sleeve 122. Thisarcuate collar 132c has a unidirectionally sloped tooth 132d whichengages similarly shaped notches 132e in the lower edge of the circularcollar 132a. A flange 132f extending from the arcuate collar 132c has adownwardly extending pin 132g which engages a hole 110 in the lower ring108. A helical spring 132h wound coaxially about this pin 132g upwardlybiases the arcuate collar 132c. Thus, as the sleeve 122, and thereforethe circular collar 132a, is rotated, the mating tooth 132d and notches132e allow the sleeve 122 to rotate in one direction only.

This ratchet assembly 132 advantageously allows the sleeve 122 to berotated in calibrated amounts, e.g. by listening for the "clicks" madeas the tooth 132d snaps into place when engaging one of the notches 132eas the sleeve 122 is rotated. This allows the user of the externalfixator 100a to make calibrated adjustments of the distractor mechanism102a without the aid of tools and without the need for countingfractional revolutions of the sleeve 122. Instead, the number of clickscan be counted to determine if and when sufficient adjustment has beenmade.

Referring to FIG. 4, an external fixator assembly 100b for performinglinear distraction with an alternative preferred embodiment of a lineardistractor assembly in accordance with the present invention includeslinear distractor mechanisms 102b of an alternative type, and upper 106and lower 108 external fixator frame members, or rings, as discussedabove. This type of linear distractor mechanism 102b is particularlyuseful in those cases where the initial, or starting, distance betweenthe rings 106, 108 and the amount of lengthening are small. In suchcases, the single-threaded rod 120 is secured to one ring 106 with twonuts 126a, 126b, as discussed above, and is passed through a hole 110 inthe other ring 108 and is secured thereto with two plastic prevailingtorque lock nuts 136a, 136b which are tightened against opposing sidesof the ring 108. The faces of the plastic nuts 136a, 136b are alignedfor simultaneous interfacing with and turning in the desired directionby a double wrench 138.

Referring to FIGS. 5 and 6, an external fixator assembly 100c forperforming linear distraction with another alternative preferredembodiment of a linear distractor assembly in accordance with thepresent invention includes linear distractor mechanisms 102c of analternative type, and upper 106 and lower 108 external fixator framemembers, or rings, as discussed above. Each distractor mechanism 102cincludes the single-threaded rod 120 which is coaxial with a nonrotatingsleeve 122d. The nonrotating sleeve 122d serves as a stationary basemember and is connected to the lower ring 108 with a bolt 124c whichmates with the internal locking threads 122c. A metal C-shaped bracket140, which includes a metallic adjustment surface, is connected to theother end of the nonrotating sleeve 122d with its internally threadedbushing end 142 mating with an externally threaded portion of thenonrotating sleeve 122d.

One end of the single-threaded rod 120 is secured to the upper ring 106with two nuts 126a, 126b, as discussed above. The other end of thesingle-threaded rod 120 extends through holes 146, 144 in the topportion and bushing end 142 of the bracket 140, and is secured to thebracket 140 with a pair of plastic prevailing torque lock nuts 136a,136b which are tightened against opposing sides of the top portion ofthe bracket 140. The faces of the plastic nuts 136a, 136b are preferablyaligned for simultaneous interfacing with and rotation by theaforementioned double wrench 138.

Referring to FIGS. 7 and 8, an external fixator assembly 100d forperforming linear distraction with still another alternative preferredembodiment of a linear distractor assembly in accordance with thepresent invention includes linear distractor mechanisms 102d of analternative type, and upper 106 and lower 108 external fixator framemembers, or rings, as discussed above. Each distractor mechanism 102dincludes the single-threaded rod 120 which is coaxial with a nonrotatingsleeve 122e. The nonrotating sleeve 122e serves as a stationary basemember and is connected to the lower ring 108 with a bolt 124c whichmates with the internal locking threads 122c.

One end of the single-threaded rod 120 is secured to the upper ring 106with two nuts 126a, 126b, as discussed above. The other end of thesingle-threaded rod 120 extends and threads into a threaded, rotatableplastic insert 148 within the nonrotating sleeve 122e. The plasticinsert 148 is captured within the nonrotating sleeve 122e and preventedfrom being withdrawn therefrom by crimping the sleeve 122e after theinsert 148 has been pressed therein. The plastic insert 148 includes ashaped (e.g. square) portion 150 which can be used as a tool interfacefor mating with the aforementioned wrench 134.

As should be evident from the foregoing, the metal-to-plastic interfacesbetween the rod 120, bracket 140 and plastic nuts 136a, 136b (FIG. 5),and between the rod 120, sleeve 122e and plastic insert 148 (FIG. 7),allow the plastic nuts 136a, 136b and plastic insert 148 to beselectively rotated while simultaneously forming and maintaining a rigidstructure with respect to the upper 106 and lower 108 rings.

Referring to FIG. 9, an external fixator 200 for performing angulardistraction with a preferred embodiment of an angular distractorassembly in accordance with the present invention includes upper 106 andlower 108 external fixator rings (as discussed above), an angulardistractor mechanism 202, and two pivotable, or hinged, spacermechanisms 204. The upper 106 and lower 108 rings have an angularorientation with respect to one another which is determined by thedistractor mechanism 202 and pivotable spacer mechanisms 204.

Each pivotable spacer mechanism 204 includes a threaded rod 212 which isfastened to the upper ring 106 by two nuts 216 tightened on opposingsides thereof. The bottom of the threaded rod 212 includes a sphericalprofile and is anchored in a pivotable connector assembly 214, which inturn is fastened to the bottom ring 108 by a bolt (not shown) threadedinto its underside through a hole 110 of the bottom ring 108.

The pivotable connector assembly 214 includes a metal frame 214a with aplastic insert 214b. A set screw 214d is tightened snugly against thespherically-profiled portion (or "ball") of the threaded rod 212 to holdit in place within the plastic insert 214b. For additional strength asdesired, the plastic insert 214b can include a metal core 214c intowhich the set screw 214d is threaded. The threaded rod 212 protrudesthrough a circumferential slot 214e in the metal frame 214a. This allowsthe threaded rod 212 to pivot along an arc extending outwardly from thepivot axis formed by the longitudinal axis of the plastic insert 214b(i.e. coaxial with the set screw 214d).

The angular distractor mechanism 202 includes a single-threaded rod 220which is coupled to the top ring 106 by an upper pivotable connectorassembly 208, and coupled to the lower ring 108 by a lower pivotableconnector assembly 206. The upper 208 and lower 206 pivotable connectors(discussed further below) are fastened to the upper 106 and lower 108rings by bolts 210. As discussed further below, a rotatable knob 218 isaffixed to and used to rotate the threaded rod 220. This causes theupper pivotable connector 208, which is threaded onto the rod 220, totravel along the length of the rod 220. This, in turn, causes the upper208 and lower 206 pivotable connectors to be selectively drawn closertogether or further apart. This action, in conjunction with the pivotingaction of the pivotable spacers 204, allows the angular orientationbetween the upper 106 and lower 108 rings to be adjusted. The pivotablespacers 204 are mounted on the lower ring 108 so as to make theirpivotal axes collinear with one another.

Referring to FIG. 10, the angular distractor mechanism 202 can be betterunderstood. As shown, the threaded rod 220 is threaded into a plasticinsert 208b which is captured within the metal frame 208a of the upperpivotable connector 208. The frame 208a has a circumferential slot 208c(FIG. 9) to allow arcuate movement of the threaded rod 220 as it and theplastic insert 208b rotate within the frame 208a during distractionadjustments.

The bottom of the threaded rod 220 (with the spherically-profiled, or"ball", portion) is inserted into and anchored within a plastic spacer206b captured within the metal frame 206a of the lower pivotableconnector 206. The bottom of the threaded rod 220 is anchored within theplastic spacer 206b by way of a hex-socket set screw 206c which isthreaded into the plastic insert 206b (which can include a metal core206d for additional strength). As discussed further below, the set screw206c has a cup-shaped tip which engages the base of the rod 220 andallows the rod 220 to rotate about its longitudinal axis within theplastic insert 206b. Similar to the upper pivotable connector 208, thelower pivotable connector frame 206a has a circumferential slot 206e(FIG. 9) which allows arcuate movement of the threaded rod 220 duringdistraction adjustments.

Referring to FIGS. 10, 11 and 12, the rotatable knob 218 has an innercoaxial plate 218a which is fixed to the threaded rod 220 viacompression with a hex-socket set screw 218b. A coaxial sleeve 218c,surrounding the plate 218a, is biased downwardly by two springs 218d butcan be pulled upwardly, due to an elongated clearance hole, or slot,218e for the set screw 218b.

When biased downwardly by the springs 218d, the sleeve 218c sits atopthe upper portion of the frame 206a of the lower pivotable connector206. A square hole 218f prevents this sleeve 218c from being rotatedwhen in this position.

Referring to FIG. 13, an external fixator 300 for performing angulardistraction with an alternative preferred embodiment of an angulardistractor assembly in accordance with the present invention includesupper 106 and lower 108 external fixator rings (as discussed above), anangular distractor mechanism 202 (as discussed above), and pivotablespacer mechanisms 302.

Referring to FIGS. 13 and 14, each of the pivotable spacer mechanisms302 includes a threaded rod 304, a pivotable connector 306 and bracketassembly 308. The rod 304 is fastened to the lower ring 108 with thebracket assembly 308, which consists of a bracket frame 308a, a bolt308b and two nuts 308c. The rod 304 is pivotally connected to the upperring 106 by the pivotable connector 306. The pivotable connector 306includes a metal frame 306a which is fastened to the upper ring 106 by abolt 306b. The upper end of the rod 304 is anchored within a plasticinsert 306c captured within the metal frame 306a by way of hex-socketset screw 306d which is threaded through the plastic insert 306c (whichcan include a metal core 306e for additional strength). The metal frame306a includes a circumferential slot 306f to allow arcuate movement ofthe rod 304 during distraction adjustments.

Referring to FIG. 15, the pivotable connectors 306 are aligned with oneanother so as to make their axes of rotation collinear with one another.

Due to the metal-to-plastic interfaces of the rods 212, 220 (FIG. 9),304 (FIG. 13) and connectors 206, 208, 214 (FIG. 9), 306 (FIG. 13),angular distraction adjustments can be made while simultaneously formingand maintaining a rigid structure with respect to the interconnectedupper 106 and lower 108 rings.

In accordance with the present invention, the threaded rods 120 (FIGS.1, 5 and 7), 212 (FIG. 9), 220 (FIG. 9) and 304 (FIG. 13) are metal,preferably stainless steel. The rotatable sleeve 122 (FIG. 1) andnonrotating sleeves 122d, 122e (FIGS. 5 and 7) are metal, preferablyaluminum. The various plastic inserts 128 (FIG. 1), 148 (FIG. 7), 208b,214b (FIG. 9), 206b (FIG. 10), 306c (FIG. 13), plastic washers 124a,124b (FIG. 2), and plastic nuts 136a, 136b (FIGS. 4 and 5) arepreferably nylon (e.g. Nylon 6/6) polyphenylene sulfide, polyamid orpolyimid. However, other plastics having similar resiliency qualitiescan be used as well.

Referring to FIGS. 16, 17 and 18, the fastener assembly 112 for thewires 114 and/or half-pins 116 can be better understood. Each fastenerassembly 112 includes a bolt 112a and a nut 112b. The bolt 112a has athreaded shaft 112c which is inserted through one of the holes 110 ofthe ring 106/108, and onto which is threaded and tightened the nut 112b.The bolt 112a also has a shank 112d with a transverse bore 112e. It isinto this bore 112e that the wire 114 or larger diameter half-pin 116 isinserted.

The transverse shank bore 112e is asymmetrical with respect to themounting surface for the fastener assembly 112, i.e. the plane of thering 106/108. As can be seen, the bore 112e has a minimum radius RMINand a maximum radius RMAX, with the minimum radius RMIN directed towardthe threaded shaft 112c and the maximum radius RMAX directed toward thehead of the bolt 112a. Preferably, the bore 112e is a teardrop-shapedhole as shown, but other asymmetrical shapes can be used as desired.

It can seen that such an asymmetrical hole 112e advantageously providesconsistent contact surfaces for contacting and securing the wire 114 orhalf-pin 116, regardless of their diameters. Accordingly, the samefastener assembly 112 can be used for wires 114 and/or half-pins 116having a large variety of diameters.

From the foregoing, it can be seen that the inboard pivots, or hinges,provided by the pivotable spacers 204 of FIG. 9 provide an axis ofrotation which is parallel to the plane formed by the lower ring 108 andis located between the planes formed by the upper 106 and lower 108rings. Further, it can be seen that the outboard pivots, or hinges,formed by the pivotable spacers 302 of FIG. 13 form an axis of rotationwhich lies approximately within the plane formed by the upper ring 106.Accordingly, it should be understood that various combinations of theseinboard 204 and outboard 302 pivotable spacers can be used to performvarious forms of angular distraction of bone segments. Additionally, itshould be recognized that the terms "upper" and "lower" with respect tothe two external fixator rings 106, 108 have been used for purposes ofconvenience only, and are not to be construed as limitations upon theiractual location or orientation with respect to one another.

Various other modifications and alterations in the structure and methodof operation of this invention will be apparent to those skilled in theart without departing from the scope and spirit of this invention.Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiments.

We claim:
 1. An external fixation device having a distraction mechanism,the external fixation device disposed to immobilize a bone fractureduring distraction thereof, the distraction mechanism comprising:firstand second external fixator frame members separated by means foradjusting linear separation therebetween, said means for adjustingincluding: a threaded rod, the threaded rod rigidly connected to thefirst external fixator frame member and extending towards the secondfixator frame member, the threaded rod received into an opening in ametallic adjustment surface wherein telescopic displacement of themetallic adjustment surface with respect to the threaded rod causescorresponding adjustment of linear separation between the first andsecond external fixator frame members; and a pair of plastic nuts eachthreadably engaged on the threaded rod and disposed either side of themetallic adjustment surface, wherein tightening of the plastic nuts downon the metallic adjustment surface forms a rigid connection between thefirst and second external fixator frame members, and wherein synchronousco-rotation of the plastic nuts after said tightening adjusts linearseparation between the first and second external fixator frame memberswithout introducing play in said rigid connection between the first andsecond external fixator frame members.
 2. The external fixation deviceof claim 1, in which the metallic adjustment surface is integral to thesecond external fixator frame member.
 3. The external fixation device ofclaim 2, wherein said metallic adjustment surface is located on aC-shaped bracket.
 4. The external fixation device of claim 3, whereinsaid C-shaped bracket is attached to a sleeve, with an internallythreaded bushing end of said bracket mating with an externally threadedend of said sleeve, wherein said externally threaded end of said sleeveis distally located from said second external fixator frame member. 5.The external fixation device of claim 1, in which the second externalfixator frame member has an extension rigidly connected thereto andextending towards the first external fixator frame member, and in whichthe metallic adjustment surface is located on the second externalfixator frame member extension.
 6. The external fixation device of claim1, in which the plastic nuts have outer faces, and in which the outerfaces of each plastic nut are aligned following said tightening toenable a double wrench to perform said synchronous co-rotation thereof.7. The external fixation device of claim 1, wherein said rigidconnection between said threaded rod and said first external fixatorframe member comprises:a hole in the first external fixator framemember, wherein said threaded rod is received therein; and a pair ofnuts received onto said threaded rod and disposed on opposing sides ofsaid first external fixator frame member.
 8. An external fixation devicehaving a distraction mechanism, the external fixation device disposed toimmobilize a bone fracture during distraction thereof, the distractionmechanism comprising:first and second external fixator frame membersseparated by means for adjusting linear separation therebetween, saidmeans for adjusting including: a threaded rod, the threaded rod rigidlyconnected to the first external fixator frame member and extendingtowards the second fixator frame member, the threaded rod received intoan opening in a metallic adjustment surface integral to the secondexternal fixator frame member wherein telescopic displacement of themetallic adjustment surface with respect to the threaded rod causescorresponding adjustment of linear separation between the first andsecond external fixator frame members; and a pair of plastic nuts eachthreadably engaged on the threaded rod and disposed either side of themetallic adjustment surface, wherein tightening of the plastic nuts downon the metallic adjustment surface forms a rigid connection between thefirst and second external fixator frame members, and wherein synchronousco-rotation of the plastic nuts after said tightening adjusts linearseparation between the first and second external fixator frame memberswithout introducing play in said rigid connection between the first andsecond external fixator frame members; and the plastic nuts furtherhaving outer faces, wherein the outer faces of each plastic nut arealigned following said tightening to enable a double wrench to performsaid synchronous co-rotation thereof.
 9. A method for distraction of abone fracture, comprising the steps of:(a) immobilizing a bone fracturewith an external fixation device having first and second externalfixator frame members; and (b) distracting the bone fracture byadjusting linear separation between the first and second externalfixator frame members, wherein step (b) includes the substeps of:(i)rigidly connecting a threaded rod to the first external fixator framemember and extending the threaded rod towards the second fixator framemember; (ii) receiving the threaded rod into an opening in a metallicadjustment surface wherein telescopic displacement of the metallicadjustment surface with respect to the threaded rod causes correspondingadjustment of linear separation between the first and second externalfixator frame members; (iii) threadably engaging a pair of plastic nutson the threaded rod; (iv) disposing the plastic nuts either side of themetallic adjustment surface; (v) forming a rigid connection between thefirst and second external fixator frame members by tightening theplastic nuts down on the metallic adjustment surface; and (vi)synchronously co-rotating the plastic nuts after said tightening tocause corresponding adjustment of linear separation between the firstand second external fixator frame members without introducing play insaid rigid connection between the first and second external fixatorframe members.
 10. The method of claim 9, in which the metallicadjustment surface is integral to the second external fixator framemember.
 11. The method of claim 10, wherein said metallic adjustmentsurface is located on a C-shaped bracket.
 12. The method of claim 11,further comprising the step of:attaching said C-shaped bracket to asleeve, with an internally threaded bushing end of said bracket matingwith an externally threaded end of said sleeve, wherein said externallythreaded end of said sleeve is distally located from said secondexternal fixator frame member.
 13. The method of claim 9, in which thesecond external fixator frame member has an extension rigidly connectedthereto and extending towards the first external fixator frame member,and in which the metallic adjustment surface is located on the secondexternal fixator frame member extension.
 14. The method of claim 9, inwhich the plastic nuts have outer faces, and in which step (b) includesthe further substep of:(vii) aligning the outer faces of each plasticnut following said tightening to enable a double wrench to perform saidsynchronous co-rotation.
 15. The method of claim 9, wherein said step ofrigidly connecting said threaded rod to said first external fixatorframe member further comprises the step of:receiving said threaded rodthrough a hole in said first external fixator frame member; andthreadably disposing a pair of nuts onto said threaded rod on opposingsides of said first external fixator frame member.